Method of manufacturing a golf ball

ABSTRACT

A golf ball is made by a process comprising:  
     grinding a core of another golf ball into powder rubber in which more than 30% of particle is 0.8 mm or more in an average particle diameter, the another golf ball covered with one or more layers, in which 40 mass parts or less of metal salt of α,β unsaturated fatty acids is compounded to 100 mass parts diene rubber;  
     preparing a core of the golf ball by kneading 0.1 to 30 mass parts of the powder rubber with a core material in which 40% mass parts or less of metal salt of α,β unsaturated fatty acids is compounded to 100 mass parts diene rubber; and  
     covering the core of the golf ball with one or more layers.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a golf ball having low repulsion, and particularly to a solid golf ball that is superior in a function of a training golf ball and easy to be recycled.

[0003] 2. Description of the Related Art

[0004] As a golf ball, a conventional winding ball is not used gradually but a so-called solid ball is mainly used. Namely, as a solid ball, a two-piece or multi-piece ball in which the periphery of a core is covered with at least one-layered cover is put to practical use. Further, also in a training golf ball, the solid ball is mainly used, and one-piece ball formed of only core or a multi-piece ball in which the periphery of a core is covered with at least one-layered cover is used. Regarding performance target of this training golf ball, usually a shot feeling is set the same and a flying distance is set somewhat low, compared with those of a normal ball.

[0005] Further, mixing of powder rubber into the training golf ball is proposed. Furthermore, when the training golf ball finished its business, it is ideal to use this ball itself as recycled resources, whereby it is possible to use resources effectively and to reduce cost of production more.

[0006] However, in case that the conventional ball in which mixing of powder rubber is proposed is referred to the aforesaid performance target of training golf ball, this performance target is not always achieved sufficiently. Therefore, various improved balls have been proposed heretofore.

[0007] For example, a golf ball having high repulsion, no decrease of flying distance and improved shot feeling is proposed in Japanese Patent Registration No. 2741338, wherein the golf ball has a core formed by mixing 100 mass parts of rubber component of a core material, in which 25 to 40 mass parts or more of metal salt of α,β unsaturated fatty acids is compounded to 100 mass parts of diene rubber, with 35 to 150 mass parts of vulcanized rubber powder having an average particle diameter of 0.01 to 0.8 mm that is obtained by grinding a golf ball core, in which 60 to 120 mass parts of metal salt of α,β unsaturated fatty acids is compounded to 100 mass parts of diene rubber.

[0008] However, in this proposal, since the mixing amount of the powder rubber is large, mixing efficiency is extremely bad and there is fear that durability of ball decreases extremely. Further, since the average particle diameter is too small, there is a difficulty that manufacturing cost of powder rubber increases.

[0009] Further, since the amount of metal salt of α,β unsaturated fatty acids compounded into the core rubber of the golf ball is very large (60 to 120 mass parts), the core compound of the ball becomes special and it is impossible to reuse the core rubber of the ready-used ball, so that there is a defect that the continuity of recycle stops.

[0010] On the other hand, recently, a solid ball having multi-layer structure is increasingly used as a normal ball (i.e., course ball) in order to optimize shot feeling, durability and flying distance. In addition, also a training golf ball has a similar tendency.

[0011] Accordingly, in view of the above circumstances, an object of the invention is to provide a high-repulsion multi-piece golf ball in which its manufacture is easy, durability and hit feeling are particularly superior, and a flying distance is shorter a little than that of a normal golf ball.

SUMMARY OF THE INVENTION

[0012] In order to solve the above problems and achieve the object, in a first aspect of the invention, a golf ball is made by a process comprising:

[0013] grinding a core of another golf ball into powder rubber in which more than 30% of particle is 0.8 mm or more in an average particle diameter, the another golf ball covered with one or more layers, in which 40 mass parts or less of metal salt of α,β unsaturated fatty acids is compounded to 100 mass parts diene rubber;

[0014] preparing a core of the golf ball by kneading 0.1 to 30 mass parts of the powder rubber with a core material in which 40% mass parts or less of metal salt of α,β unsaturated fatty acids is compounded to 100 mass parts diene rubber; and

[0015] covering the core of the golf ball with one or more layers.

[0016] In the golf ball according to the invention, the amount of the metal salt of α,β unsaturated fatty acids compounded into the diene rubber mixed with the powder rubber is set to 40 mass parts or less. Therefore, the hardness of core rubber does not become too hard and hit feeling is soft, that is, hit feeling improves.

[0017] However, in case that the amount of the compounded metal salt of α,β unsaturated fatty acids is too small, there is fear that the repulsion of ball decreases extremely. Therefore, it is preferable that the minimum compound amount is set to 0.1 mass part.

[0018] Incidentally, as metal salt of α,β unsaturated fatty acids, there are metal salt of α,β unsaturated fatty acid such as zinc salt of α,β unsaturated fatty acid, magnesium salt of α,β unsaturated fatty acid, and the like, that is, for example, acrylic acid, methacrylic acid, and the like.

[0019] It is preferable that the amount of the powder rubber compounded to 100 mass parts of rubber component of the core material is set in a range of 0.1 to 30 mass parts, and more preferably 5 to 25 mass parts.

[0020] In case that the mixed amount is less than 0.1 mass parts, the basic performances of a training ball (suppression of flying distance, reduction of manufacturing cost) and the improvement of hit feeling cannot be obtained. Further, in case that the mixed amount is more than 30 mass parts, as described in an embodiment later, a golf ball is not practical in view of mixing efficiency and products performances (flying distance, durability).

[0021] Further, since the mixed amount of the powder rubber is set low, i.e., 0.1 to 30 mass parts to 100 mass parts of the rubber component of the core material, decrease of durability caused by mixing of the powder rubber is suppressed and the mixing operation when the ball is manufactured is facilitated.

[0022] Further, the powder rubber mixed in the core rubber is ground powder including 30% or more of particles which is more than 0.80 mm in the average particle diameter. Therefore, the powder rubber can be obtained by a comparatively easy manufacturing method, and manufacturing cost of the powder rubber becomes low.

[0023] In case that a mixing ratio of the powder particle having the average particle diameter over 0.80 mm is less than 30% and a mixing ratio of the powder particle having the average particle diameter of 0.80 mm or less is more than 70%, a special process (for example, freezing operation) or a special device is required for grinding operation. Therefore, the manufacturing method is not facilitated and the manufacturing cost of the powder rubber becomes high.

[0024] The average particle diameter of powder rubber is an average of values obtained by measuring, regarding each particle as a sphere, diameters of spheres of 100 particles selected at random from the ground powder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0025] An Embodiment of the invention will be described below.

[0026] The compound shown in Table 1 is a typical compound of a core used in a golf ball on the market. TABLE 1 Core material 1.4-cis-polybutadiene 100 (mass part) Oxide zinc 30 Acrylic zinc 35 Autioxidant 0.1 Dicumyl peroxide 0.6

[0027] Firstly, a plurality of used two-piece golf balls, which is composed of a core having the compound as shown in Table 1 and one-layered cover, Surlyn (merchandise name: HIMILAN 1706 by Du Pont-Mitsui Co., Ltd.), covering the core, are collected and are grind-selected by a known grind-selection device to manufacture a powder rubber composed of only the ground powder of core rubber.

[0028] As shown in Table 1, in a core of the used two-piece golf ball adopted in the embodiment, the compound amount of zinc acrylate as one of metal-salt of α,β unsaturated fatty acids to 100 mass parts of 1,4-cis-polybutadiene as diene rubber is 35 mass parts.

[0029] In case that the compound amount of the metal salt of α,β unsaturated fatty acids exceeds 40 mass parts, the core becomes too hard. Therefore, this compound amount of the ball on the market is almost 40 mass parts or less.

[0030] The ground powder of the core rubber ground as described above is adjusted so as to include about 30% particles having the average particle diameter larger than 0.80 mm and about 70% particles having the average particle diameter of 0.8 mm or less.

[0031] Next, the powder rubber composed of the ground powder of the core rubber is mixed in a new non-vulcanized core material having the nearly same compound as that shown in Table 1 and kneaded by a kneader.

[0032] In this case, a mixed amount of the powder rubber is 10 mass parts in a first embodiment, 20 mass parts in a second embodiment, and 30 mass parts in a third embodiment to 100 mass parts of rubber component of the new non-vulcanized core material.

[0033] In order to confirm an upper limit of the mixed amount, taking the mixed amount as 35 mass parts and 50 mass parts, trial was performed. However, in this case, in a rubber mixing process, the rubber did not crunch into a rotor of a mixer, and the working efficiency worsened remarkably, so that it was confirmed that these mixed amounts could not be applied to practical use.

[0034] Next, the core rubber in which the powder rubber was mixed as described above was vulcanization-molded into a globular shape by using a predetermined metal mold under a predetermined vulcanized condition. Thereafter, this was placed in the center of another predetermined metal mold, and one-layered Surlyn cover was injection-molded on an outer surface of the core by an injection-molding machine, so that a two-piece golf ball in each embodiment was molded.

[0035] Further, as a comparative example, a normal golf ball in which the compound of core rubber is the same as that in the embodiment and the powder rubber is not added was manufactured simultaneously in the same molding process as that in the embodiment.

[0036] Next, on golf balls in these embodiments and comparative example, a test of products performance was executed on a basis of each test method and condition described out of a Table 2. TABLE 2 Comparative example Embodiment 1 Embodiment 2 Embodiment 3 Powder Mixed amount 0.0 10.0 20.0 30.0 rubber (mass portion) Mixing ⊚ ⊚ ⊚˜◯ ◯ efficiency Products OD mm 42.70 42.71 42.69 42.70 Weight (gf) 45.20 45.19 45.20 45.22 Hardness mm 2.60 2.52 2.48 2.45 Initial m/s 77.35 77.28 77.10 77.01 speed Flying HS45 Carry 210.0 208.0 209.0 205.0 performance #W1 Total 221.0 219.0 218.0 214.5 HS35 Carry 145.0 142.0 140.0 141.5 #W1 Total 156.5 153.0 152.0 150.0 Durability Crack start 360 times 331 times 304 times 280 times Crack average 403 times 382 times 391 times 332 times

[0037] Results of the test are shown in the Table 2 together with an evaluation of mixing efficiency in manufacture.

[0038] Weight and outer diameter of a ball in each embodiment is nearly the same as those in the comparative example.

[0039] Than the ball in the comparative example, each balls in the embodiments is smaller in hardness of core (represented by distortion amount mm when 130 Kg compression load is applied), and become smaller in the hardness of core as the mixed amount of the powder rubber increases, which shows that hit feeling becomes harder and worse with increase of the mixed amount.

[0040] Further, in the golf balls according to the embodiments, an initial speed of shot ball is low. In case that head speed of a driver club is 45 m/s and 35 m/s, flying performance, that is, flying distance (carry, total) is smaller with the increase of the mixed amount of the powder rubber.

[0041] Carry of the training golf ball is set so that the total carry is shorter than that of the normal ball (course ball) by about 10 m at lower limit.

[0042] Further, in a hit-durability test, it was confirmed that as the mixed amount of powder rubber increased, the crack-durability of ball gradually decreased, and it was found that limit of the above mixed amount was 30% mass parts. Further, lower limit of crack-durability is about 200 times from experience.

[0043] Further, regarding the mixing efficiency in manufacture, the result shows that the case in the third embodiment is a limit of mixed amount in view of easiness of crunching into the rotor of the kneader.

[0044] Further, it is appropriate from the past empirical results that the decrease amount of the flying distance of the training ball in relation to the normal ball is about 10 m. With regarding to the durability in the above hitting test, it is required that cracks are not produced up to 200 hits. Therefore, in case that the performance of each ball according to the embodiments is evaluated in consideration of this requirement, the ball according to each embodiment has a function of training ball in a balanced manner, and is easy to manufacture. Therefore, it was confirmed that a good training ball could be provided by the invention.

[0045] According to the invention, a core in which 40 mass parts or less of metal salt of α,β unsaturated fatty acids to 100 mass parts of diene rubber is compounded is ground into powder rubber including more than 30% particles being 0.80 mm or more in the average particle diameter, and 0.1-30 mass parts of this powder rubber is mixed in a core material in which 40 mass parts or less of metal salt of α,β unsaturated fatty acids to 100 mass parts of diene rubber is compounded, thereby to mold a core. And, this molded core is covered with one or more layers to mold a golf ball. Therefore, it is possible to provide a golf ball that is superior in durability and hit feeling, easy in a mixing operation and manufacture, and low in repulsion.

[0046] Particularly, according to the invention, it is possible to provide a golf ball that has a function of a training golf ball in a balanced manner and sufficiently. Further, since it is easy to reuse the ball as a powder rubber, recyclability improves. 

What is claimed is:
 1. A golf ball made by a process comprising: grinding a core of another golf ball into powder rubber in which more than 30% of particle is 0.8 mm or more in an average particle diameter, the another golf ball covered with one or more layers, in which 40 mass parts or less of metal salt of α,β unsaturated fatty acids is compounded to 100 mass parts diene rubber; preparing a core of the golf ball by kneading 0.1 to 30 mass parts of the powder rubber with a core material in which 40% mass parts or less of metal salt of α,β unsaturated fatty acids is compounded to 100 mass parts diene rubber; and covering the core of the golf ball with one or more layers.
 2. The golf ball according to claim 1, wherein an amount of the powder rubber compounded to the core material is 5 to 25 mass parts. 